1. Field of the Invention
The present invention relates to an oil sorbent made of fibrous ligno-material.
As seen from the Gulf War, stranding of an oil tanker and the like, marine pollution with an oil makes severe environmental disruption. Pollution due to an oil floating on or suspending in an industrial or domestic waste water also makes cumbersome problem. The present invention relates to an oil sorbent for efficiently adsorbing an oil which cause such pollutions.
2. Discussion of Background
With respect to collection and removal an oil floating on water therefrom, various methods are known, for example, a method which comprises pumping a mixture water with an oil, followed by emulsification with an emulsifier. Of these, a method which comprises causing a floating oil to be captured by means of an oil sorbent to effect collection and removal of the oil is the most simple and effective method.
Those used as such an oil sorbent for an oil floating on water are required to be good in hydrophobicity as well as in lipophilicity. As the material having such properties, synthetic resins such as a polypropylene and a polyurethane are widely used. As natural materials, there have been proposed one obtained by rendering a hydrophilic lignocellulose hydrophobic (Japanese Examined Patent Publication No.23702/1969), a ground wood piece having its surface sized with a paraffin wax (Japanese Examined Patent Publication No.15279/1979), one obtained by binding a polyvalent metal salt with a phosphoric acid-treated pulp and causing the polyvalent metal salt to be retained with a paraffin wax (Japanese Examined Patent Publication No.51386/1985), and a carbonized cellulosic fiber (Japanese Unexamined Patent Publication No.5893/1974). Further, since silky fibers of a seed of a kapok tree which grows in Southeast Asia (Java cotton)are highly hydrophobic and adequately lipophilic, Java cotton fixedly adhered to a polyethylene or polypropylene matrix is also known (Japanese Examined Patent Publication No.8033/1985).
Moreover, the applicant of the present application has previously filed a patent application relating to an oil sorbent which enables drawbacks inherent in such conventional inventions to be remedied (Japanese Patent Application No.70672/1993).
An oil sorbent for adsorbing an oil floating on water is required not only to have excellent adsorptivity as described above but also to be guaranteed in availability for its starting material, prepared in a simple manner, and excellent in disposal after being used. However, the above-mentioned conventional oil adsorbents using a synthetic resin such as a polypropylene or a polyurethane have problems in disposal after being used that a special incinerator is required when they are subjected to thermal disposal and, on the other hand, that they obstinately remain undecomposed if buried under the ground. On the other hand, with respect to the oil sorbent derived from natural materials such as one obtained by rendering a hydrophilic lignocellulose hydrophobic (Japanese Examined Patent Publication No.23702/1969), a ground wood piece having its surface sized with a paraffin wax (Japanese Examined Patent Publication No.15279/1979), and one obtained by binding a polyvalent metal salt with a phosphoric acid-treated pulp and causing the polyvalent metal salt to be retained with a paraffin wax (Japanese Examined Patent Publication No.51886/1985), there are the following problems. The natural materials per se are not effective as an oil sorbent and it is, therefore, necessary to intentionally impart water repellency thereto. If complicated treatment is required to impart water repellency, high costs are resulted therefrom. Further, when the natural materials are procured by import, stable availability for the starting material is not necessarily expectable.
In particular, it is described in the above-mentioned Japanese Unexamined Patent Publication No.5893/1974 that with respect to the oil sorbent disclosed therein which is a carbonized cellulosic fiber, addition of a reaction accerator such as NH.sub.4 Br is effective in order to reduce a carbonization temperature. It is, however, described therein that the use of the reaction accerator involves disadvantageously strengthened water absorption properties of the resulting carbonized fiber ( see Japanese Unexamined Patent Publication No.5893/1974, column 3, line 5) and accordingly "use of a water repellant" is necessary to promote water repellency (see Japanese Unexamined Patent Publication No.5893/1974, column 5, line 18). Further, the cellulosic fiber of the invention disclosed therein means a regenerated cellulosic fiber such as a rayon staple, and a fiber of this type no longer has a hollow structure including a number of voids in the form of a natural fiber. The production of this oil sorbent has drawbacks that the step of regeneration of cellulose is required and yet treatment for imparting water repellency with a water repellant is troublesomely required, thereby leading to an increased cost.
With respect to an oil sorbent which is capable of eliminating the above-mentioned drawbacks inherent in such prior art techniques, the applicant of the present application has filed a patent application as Japanese Patent Application No.70672/1993. However, the "oil sorbent" according to this application has an unsolved problem that when it is allowed to float in water for a long period of time, its density gradually becomes high as it absorbs water and finally a portion of it sinks under the water surface. It goes without saying that as an oil sorbent used in a large extent of sea or the like, one capable of floating on water for a long period of time is practically preferred from the operational viewpoint. Further, to reduce production cost of an oil sorbent, a device is required which is capable of continuously producing the oil sorbent in a short time.